Diabetes mellitus is a disease of major global importance, increasing in frequency at almost epidemic rates, such that the worldwide prevalence in 2006 is 170 million people and predicted to at least double over the next 10-15 years. Diabetes is characterized by a chronically raised blood glucose concentration (hyperglycemia), due to a relative or absolute lack of the pancreatic hormone, insulin. Within the healthy pancreas, beta cells, located in the islets of Langerhans, continuously produce and secrete insulin according to the blood glucose levels, maintaining near constant glucose levels in the body.
Much of the burden of the disease to the user and to health care resources is due to the long-term tissue complications, which affect both the small blood vessels (microangiopathy, causing eye, kidney and nerve damage) and the large blood vessels (causing accelerated atherosclerosis, with increased rates of coronary heart disease, peripheral vascular disease and stroke). The Diabetes Control and Complications Trial (DCCT) demonstrated that development and progression of the chronic complications of diabetes are greatly related to the degree of altered glycemia as quantified by determinations of glycohemoglobin (HbAlc). [DCCT Trial, N Engl J Med 1993; 329: 977-986, UKPDS Trial, Lancet 1998; 352: 837-853. BMJ 1998; 317, (7160): 703-13 and the EDIC Trial, N Engl J Med 2005; 353, (25): 2643-53]. Thus, maintaining normolycemia by frequent glucose measurements and adjustment of insulin delivery accordingly is of utmost importance.
Insulin pumps deliver rapid acting insulin 24 hours a day through a catheter placed under the skin. The total daily insulin dose is divided into basal and bolus doses. Insulin bolus doses are delivered before or after meals to counteract carbohydrates loads or during episodes of high blood glucose levels (correction boluses “CB”). The amount of insulin in the administered bolus depends on several parameters:                Amount of carbohydrates (Carbs) to be consumed        Carbohydrate-to-insulin ratio (CIR), i.e. the amount of carbohydrates balanced by one unit of insulin        Insulin sensitivity (IS), i.e. the amount of blood glucose level lowered by one unit of insulin.        Current blood glucose level        Target blood glucose (TBG) level (i.e. the desired blood glucose level). TBG for most diabetes patients is in the range of 90-130 mg/dL before a meal, and less than 180 mg/dL 1-2 hours after the beginning of a meal.        Residual insulin (RI), i.e. the amount of stored insulin remained in the body after recent bolus delivery that is still active. This parameter is relevant when there is a short time interval between consecutive bolus doses (e.g. less than 5 hours).        
Basal insulin can be delivered continuously over 24 hours, and can keep the blood glucose concentration levels (namely, blood glucose levels) in normal desirable range between meals and overnight. Diurnal basal rates can be pre-programmed or manually changed according to various daily activities. Although basal delivery should be continuously administered it is often interrupted due to periodic pump disconnection. These interruptions can hamper glycemic control and if prolonged can cause life threatening ketoacidosis (DKA).